Coatings, such as conversion coatings, can be used to protect substrates, such as metal and/or metal alloy substrates. Conversion coatings can protect the substrate from corrosion and can be used as a primer for other coatings, such as topcoats and paints. For example, the conversion coating can attach (e.g., adhere) another coating to the substrate. Thus, a conversion coating should exhibit good adhesion to the substrate and to the other coating, if present. A conversion coating formed by way of a sol-gel process is referred to herein as a “sol-gel conversion coating.”